Make a query in JSON data?

I have installed the JSON api from wordpress, so in every pages, when I add ?json=1, I've a well formatted JSON data. But can I make a query or a kind like that to retrieve for example in content, only the pictures ...? I've tested the format ?json=1&count=3&custom_fields=PostThumb&include=content, but that's not really what I want. Can we make a query to parse JSON beginning by "http://" ??? Or can I find the informations that I want on the website, and create a specific div for retrieving this information after in JSON ?

I've to retrieve three pictures from a website with wordpress and some specific content which are in the content page, and use it in iOS app with JSON.